1. Technical Field
This invention relates to reflective telescope systems and, more particularly, to an all reflective multiple field of view optical system.
2. Discussion
When viewing a distant object through a telescope system, the observer is commonly interested in performing two separate and sequential functions. The first of these functions is a coarse search over a large field of view for the purpose of locating or acquiring previously undetected objects. The second function is the fine examination over a smaller field of view for purposes of identification or discrimination of previously located objects.
A number of three mirror anastigmat telescopes which have different magnifications have been designed and implemented in the past. These designs, however, have been typically only implemented with a single field of view. An example of this type of system is illustrated in U.S. Pat. No. 3,674,334, issued Jul. 4, 1972 to Offner entitled, "Catoptric Anastigmat Afocal Optical System". Typically, in order to achieve a multiple field of view system, two or more telescopes are used. Each of the telescopes has its own separate and distinct entrance aperture region, optical path, packaging volume, and exit pupil plane. These configurations take up an enormous amount of space and/or volume. Hence, there is a desire for a system which minimizes the space requirements by sharing a common volume and providing a multiple field of view system.
An example of a three mirror anastigmat telescope which has different magnifications and utilizes a common entrance aperture region, packaging volume, and exit pupil plane is illustrated in Applicant's co-pending U.S. patent application Ser. No. 525,801 filed May 21, 1990 to Iossi et al. entitled "Wide Field All Reflective Multiple Field of View Telescope," assigned to the same assignee of the present application, the specification of which is herein incorporated by reference. This application illustrates a single telescope with a pair of three-mirror anastigmats which move with respect to one another to provide a multiple field of view optical system.
Also, refractive telescope systems have been utilized in whole or in part. Refractive optical systems generally have one or more of the following disadvantages. Refractive systems generally have spectral limitations and chromatic aberrations. Refractive systems have size limitations, lens material limitations and a lack of radiation hardness. Further, the refractive systems are more sensitive to thermal changes and are exceptionally heavy when used in large aperture designs.